package core.fire.eventbus;

import java.lang.reflect.Method;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Set;

import com.google.common.base.Objects;
import com.google.common.base.Throwables;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Maps;
import com.google.common.collect.Multimap;
import com.google.common.eventbus.AllowConcurrentEvents;
import com.google.common.eventbus.Subscribe;
import com.google.common.reflect.TypeToken;
import com.google.common.util.concurrent.UncheckedExecutionException;

public class AnnotatedSubscriberFinder implements SubscriberFindingStrategy
{
    /**
     * A thread-safe cache that contains the mapping from each class to all
     * methods in that class and all super-classes, that are annotated with
     * {@code @Subscribe}. The cache is shared across all instances of this
     * class; this greatly improves performance if multiple EventBus instances
     * are created and objects of the same class are registered on all of them.
     */
    private static final LoadingCache<Class<?>, ImmutableList<Method>> subscriberMethodsCache = CacheBuilder.newBuilder().weakKeys().build(new CacheLoader<Class<?>, ImmutableList<Method>>() {
        @Override
        public ImmutableList<Method> load(Class<?> concreteClass) throws Exception {
            return getAnnotatedMethodsInternal(concreteClass);
        }
    });

    /**
     * {@inheritDoc}
     *
     * This implementation finds all methods marked with a {@link Subscribe}
     * annotation.
     */
    @Override
    public Multimap<Class<?>, EventSubscriber> findAllSubscribers(Object listener) {
        Multimap<Class<?>, EventSubscriber> methodsInListener = HashMultimap.create();
        Class<?> clazz = listener.getClass();
        for (Method method : getAnnotatedMethods(clazz)) {
            Class<?>[] parameterTypes = method.getParameterTypes();
            Class<?> eventType = parameterTypes[0];
            EventSubscriber subscriber = makeSubscriber(listener, method);
            methodsInListener.put(eventType, subscriber);
        }
        return methodsInListener;
    }

    private static ImmutableList<Method> getAnnotatedMethods(Class<?> clazz) {
        try {
            return subscriberMethodsCache.getUnchecked(clazz);
        } catch (UncheckedExecutionException e) {
            throw Throwables.propagate(e.getCause());
        }
    }

    private static final class MethodIdentifier
    {
        private final String name;
        private final List<Class<?>> parameterTypes;

        MethodIdentifier(Method method) {
            this.name = method.getName();
            this.parameterTypes = Arrays.asList(method.getParameterTypes());
        }

        @Override
        public int hashCode() {
            return Objects.hashCode(name, parameterTypes);
        }

        @Override
        public boolean equals(Object o) {
            if (o instanceof MethodIdentifier) {
                MethodIdentifier ident = (MethodIdentifier) o;
                return name.equals(ident.name) && parameterTypes.equals(ident.parameterTypes);
            }
            return false;
        }
    }

    private static ImmutableList<Method> getAnnotatedMethodsInternal(Class<?> clazz) {
        Set<? extends Class<?>> supers = TypeToken.of(clazz).getTypes().rawTypes();
        Map<MethodIdentifier, Method> identifiers = Maps.newHashMap();
        for (Class<?> superClazz : supers) {
            for (Method superClazzMethod : superClazz.getMethods()) {
                if (superClazzMethod.isAnnotationPresent(Subscribe.class) && !superClazzMethod.isBridge()) {
                    Class<?>[] parameterTypes = superClazzMethod.getParameterTypes();
                    if (parameterTypes.length != 1) {
                        throw new IllegalArgumentException("Method " + superClazzMethod + " has @Subscribe annotation, but requires " + parameterTypes.length
                                + " arguments.  Event subscriber methods must require a single argument.");
                    }

                    MethodIdentifier ident = new MethodIdentifier(superClazzMethod);
                    if (!identifiers.containsKey(ident)) {
                        identifiers.put(ident, superClazzMethod);
                    }
                }
            }
        }
        return ImmutableList.copyOf(identifiers.values());
    }

    /**
     * Creates an {@code EventSubscriber} for subsequently calling
     * {@code method} on {@code listener}. Selects an EventSubscriber
     * implementation based on the annotations on {@code method}.
     *
     * @param listener object bearing the event subscriber method.
     * @param method the event subscriber method to wrap in an EventSubscriber.
     * @return an EventSubscriber that will call {@code method} on
     *         {@code listener} when invoked.
     */
    private static EventSubscriber makeSubscriber(Object listener, Method method) {
        EventSubscriber wrapper;
        if (methodIsDeclaredThreadSafe(method)) {
            wrapper = new EventSubscriber(listener, method);
        } else {
            wrapper = new SynchronizedEventSubscriber(listener, method);
        }
        return wrapper;
    }

    /**
     * Checks whether {@code method} is thread-safe, as indicated by the
     * {@link AllowConcurrentEvents} annotation.
     *
     * @param method subscriber method to check.
     * @return {@code true} if {@code subscriber} is marked as thread-safe,
     *         {@code false} otherwise.
     */
    private static boolean methodIsDeclaredThreadSafe(Method method) {
        return method.getAnnotation(AllowConcurrentEvents.class) != null;
    }

}
